1. Field of the Invention
The present invention relates to a pressure transducer system including a pressure sensor for accurately measuring such parameters as temperature, differential, absolute, and gauge pressures, and which is capable of detecting defects in the pressure sensor. The system includes a redundant pressure sensor and its associated circuitry.
2. Background of the Invention
Pressure transducers used to measure the pressure of a process fluid flowing through a pipe are known in the art. Pressure transducers are used in high sensitive environments such as refineries, the aerospace industry and power plants. The accurate detection of flow conditions is critical in ensuring the operation and safety of the processes in these and other industries.
Most pressure transducers are generally contained in a housing containing an inert transfer medium which isolates the process fluid being measured from the pressure sensor itself. The housing provides the sensor With resistance to corrosion which may be caused by the process fluid. Pressure is transmitted via the transfer medium to the isolated pressure sensor through diaphragms located on the housing. The diaphragms separate the process fluid from the transfer medium while permitting pressure to be transmitted to the sensor.
Pressure transducers are typically required to have their stability verified at periodic intervals to ensure that their calibration has not changed, especially in critical applications. The most likely calibration problems affecting pressure transducers are span shift and zero shift. Span shift occurs when the pressure sensitivity of the pressure sensor is no longer accurate within the normal range of operating pressures. Usually, the pressure sensitivity of the affected pressure sensor varies within the operating range. Typically, a "five valve" or a "three valve" manifold, known in the art, is used to verify the accuracy of a pressure sensor affected by span shift.
In contrast, zero shift occurs when all of the pressure sensor readings are off by some constant error value. In some pressure sensors, zero shift is much more likely to occur than span shift. Therefore, for these pressure sensors it is acceptable to check the pressure sensor only at the zero condition and compensate for any detected error shift. For example, if the pressure sensor has a reading of 1 psi at the zero condition, recalibrating the sensor would only require subtracting 1 psi from all future readings of the pressure
The present invention provides a pressure transducer system which is capable of detecting errors in the pressure sensor. Upon detection of an error, a "three valve" manifold can be used to pinpoint the cause of the error and compensate for it.